Qualification > Sciences
Edexcel BIOLOGY Doubts!!!!
Deadly_king:
--- Quote from: Blizz_rb93 on March 12, 2011, 09:21:52 am ---Thank you! :)
--- End quote ---
Anytime dude :D
Hissa:
What are the disadvantages of limitations of using a respirometer?
SoONa:
hey can someone please help me out with the fluid mosaic membrance structure .. what do i need to know??
thanks in advance
Amelia:
--- Quote from: SoONa on March 21, 2011, 09:50:54 am ---hey can someone please help me out with the fluid mosaic membrance structure .. what do i need to know??
thanks in advance
--- End quote ---
The Plasma membrane is a bi-layer of phospholipids.Each phospholipid molecule has a head that is attracted to water (hydrophilic: hydro = water; philic = loving) and a tail that repels water (hydrophobic: hydro = water; phobic = fearing). Both layers of the plasma membrane have the hydrophilic heads pointing toward the outside; the hydrophobic tails form the inside of the bilayer.
Because cells reside in a watery solution (extracellular fluid), and they contain a watery solution inside of them (cytoplasm), the plasma membrane forms a circle around each cell so that the water-loving heads are in contact with the fluid, and the water-fearing tails are protected on the inside.
Proteins and substances such as cholesterol become embedded in the bilayer, giving the membrane the look of a mosaic. Because the plasma membrane has the consistency of vegetable oil at body temperature, the proteins and other substances are able to move across it. That’s why the plasma membrane is described using the fluid-mosaic model.
The molecules that are embedded in the plasma membrane also serve a purpose. For eg:-
-The cholesterol that is stuck in there makes the membrane more stable and prevents it from solidifying when your body temperature is low. (It keeps you from literally freezing when you’re “freezing.”)
-Most proteins float about in the phospholipid bilayer forming a fluid mosaic pattern. The proteins stay in the membrane because they have regios of hydrophobic aminoacids which interact with the fatty acid tails and excludes water. The rest of the protein faces into the cell or out in the external environment, both of which are aqueous.
-Some proteins and lipids have short Carbohydrate chains like antennae forming glycoproteins and glycolipids, respectively. These carbohydrates are specific to every person, and they supply characteristics such as your blood type.
~ The Phospholipids are fluid and can move about by diffusion in their own layers.
~The mor unsaturated the tails of the phospholipid, the more fluid the membrane is.
~The membrane is about 7nm thick. ::)
Hermione Granger:
--- Quote from: SoONa on March 21, 2011, 09:50:54 am ---hey can someone please help me out with the fluid mosaic membrance structure .. what do i need to know??
thanks in advance
--- End quote ---
amelia's given a good descriptn....and il add:
the glycoproteins that are present on the cell surface membrane play a vital role in cell recognition...it helps to differentiate between bodys own cells and foreign cells...helps in immunity(but u got to know that part in A2..for AS jus knw the recognition part)!!
Also go through the basics of enzyme-working, because the working of the membrane is greatly determined by the diff in pH,temp n so on... that usually affect the workin of an enzyme...because naturally...plasma membrane has the presence of proteins n enzyme are proteins 2...(duh!.=D)..so, any changes to the pH or extreme temp above optimum, will lead to the denaturation of these proteins,and so affect the permeability of the cell.
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